Variable-dwell commutating magnetic switch construction



Oct. 25, 1966 A. C. ANSLEY VARIABLE-DWELL COMMUTATING MAGNETIC SWITCH CONSTRUCTION Filed March 12, 1965 2 Sheets-Sheet 1 INVENTOR ARTHUR Q. ANSLEY ATTORNEY A. c. ANSLEY 3,281,734

VARIABLE-DWELL COMMUTATING MAGNETIC SWITCH CONSTRUCTION Oct. 25, 1966 2 Sheets-Sheet 3 Filed March 12, 1965 L l i 38 INVENTOR United States Patent 3,281,734 VARIABLE-DWELL COMMUTATING MAGNETIC SWITCH CONSTRUCTIUN Arthur C. Ansley, Solebury Township, Bucks County, Pa., assignor to Arthur Ansley Manufacturing Company,

Bucks County, Pa., a corporation of Pennsylvania Filed Mar. 12, 1965, Ser. No. 439,149 8 Claims. (Cl. 335-152) This invention relates generally to switch mechanisms arranged in multiple for actuation by a commutator-type opera-ting element. More particularly, the invention has reference to switch mechanisms of the type referred to wherein the position of the opera-ting element can be varied to produce a wide range of adjustments, in respect to the length of time that individual switches will remain open or closed, as the case may be, and also in respect to the number of switches that are closed or open at a particular, given moment.

The invention has particular reference to reed switches. It is already common in the art to group switches of this type, and it is also known to provide for successive actuation of the switches, by exposing them in following order to a magnetic field produced by a permanent magnet mounted in close proximity to the several switches of the group.

It has been found desirable, in this regard, to permit adjustments in the length of time that each of the several switches of the group remains closed. Yet, an adjustment of this nature should be permissible without changing the total lapsed time required for a complete operating c ycle, involving actuation of all the switches of the series.

It is also desirable, in many instances, to utilize an actuating sequence of switches arranged as described above, such that there will be a make-before-break type of operation. In such a sequence, each switch of the series is caused to close before the next preceding switch opens. In this regard, the relationship should be capable of variation in such fashion that even more than two switches may be involved, that is, it may quite conceivably be desired that as regards three switches arranged in juxtaposition to one another, one switch should make before the two switches next preceding the same open.

Still further, it may be desirable to provide a controlled sequence wherein, in a single complete cycle of actuation of an annular series of switches, successively following switches should differ as regards the duration of time they remain actuated.

The main object of the present invention is to provide for the several characteristics described above. To this end, the invention, in a typical embodiment hereinafter described in detail, utilizes a commutator arm having a permanent magnet mounted on one of its ends. In accordance with the invention, the magnet is adjustable on the arm through at lea-st 90. The arm carries the adjnstably positioned magnet over a series of reed switches to actuate the same in successively following order. By selecting a particular position of adjustment for the permanent magnet, a line drawn between the poles of the magnet may be disposed anywhere from full parallelism to full perpendicularity to the long axis of each switch traversed thereby. In the presently preferred embodiment of the invention as used in association with the long, flexible contacts of a typical reed switch, the alignment of the poles of the magnet with the long axis of the switch causes the magnet to be of maximum effectiveness in extending the duration of time that a switch is actuated.

In one embodiment of the invention, the magnet may be effective to place a plurality of switches in an actuated condition simultaneously, whereby a make-before-break operation is produced.

3,281,734 Patented Oct. 25, 1966 ice In yet another form of the invention, the commutator includes an operating linkage so designed as to cause continuous angular adjustment of the magnet about its center, during a single 360 cycle of operation of the commutator. This causes progressively increasing and then progressively decreasing dwell periods, for successively following switches of the series.

Other objects will appear from the following description, the claims appended thereto, and from the annexed drawing, in which like reference characters designate like parts throughout the several views, and wherein:

FIG. 1 is a fragmentary perspective view of a printed circuit panel or card on which is mounted a switch construction according to the present invention;

FIG. 2 is an enlarged sectional view through the panel and switch structure, taken substantially on line 22 of FIG. 1;

FIG. 3 is a sectional view substantially on line 33 of FIG. 2, the full lines showing a permanent magnet actuating element in one extreme position of adjustment and the dot-ted lines showing the same in an opposite extreme position;

FIG. 4 is a View similar to FIG. 3, with the magnet disposed directly above one of the reed switches, in position to hold the switch closed for a minimum period of time;

FIG. 5 is a transverse sectional view through the commutator arm of the invention, taken substantially on line 5-5 of FIG. 4;

FIG. 6 is a plan view showing a modified construction including con-centric banks of switches each actuated by its own magnet;

FIG. 7 is a fragmentary top plan view showing a second modification, wherein a predetermined closure period for each reed switch is established through the use of a connecting linkage designed to rotate the magnet about its axis during each cycle of operation, the commutator arm being shown in full lines in one position, in dash lines in a second position, and in dash-dotted lines in a third position;

FIG. 8 is a sectional view through the modified form of FIG. 7 taken substantially on line 88 of FIG. 7; and

FIG. 9 is an enlarged transverse sectional view through the commutator arm of the modification of FIGS. 7 and 8, taken substantially on line 99 of FIG. 8.

Referring to the drawing in detail, the reference numeral 10 generally designates a reed switch assembly, according to the present invention. Switch assembly 10 in the illustrated example is mounted upon a printed circuit card or support panel 12. In the typical example shown, I provide a multiplicity of reed switches generally designated 14 uniformly, angularly spaced about a common center in an annular series, with each of the switches extending radially from said center.

The reed switches 14, per se, are well known in the art, and each of these includes (see FIG. 2) an elongated hermetically sealed glass envelope 16, in which are secured reed-type contacts 18, 20. The reed contacts extend from and are respectively secured to the opposite ends of the envelope, and have free end portions located medially between the opposite ends of the envelope. In the illustrated example, the reed switches are normally open, but the invention could be applied to normally closed switches with equal facility. Except as necessarily limited by the appended claims, it is proposed that the invention be so applied.

In any event, secured to and extending from the reed contacts 18, 20 are external, conductive connections 22, 24 respectively. The connections 22, as shown in FIG. 1, are secured to printed circuit paths or channels 26 which may be lines extending to the controlled electrical devices, not shown. The connections 24 are secured to an annular, continuous circuit path or channel 28 having a single a conductive path 30 extending thereto from a source of current, to provide a line connection.

It will be understood that this is only one type of circu1t that may be provided, and the invention is not intended to be limited to the particular circuitry illustrated in the typical, preferred embodiment shown in the several figures of the drawings.

In accordance with the invention, there is provided a commutator generally designated 32. This includes, in the illustrated, typical example, a wide, flat magnet support member in the form of an arm 34, extending radially from the center of the annular series of switches 14, in overlying relation to the switches of said series. The arm 34, at its axis of rotation, is formed with an opening in which is swaged a grommet 36 which is thus fixedly connected to the arm 34. Grommet 36 receives the outer end of a stub shaft 38 which is secured fixedly to the grommet through the provision of a set screw 40; carried by the grommet.

The stub shaft extends through and is rotatable in an opening 42 provided in the card or panel 12.

Fixedly secured to the panel 12 is a bearing sleeve 44, in which the stub shaft 38 is journaled. Shaft 38, at the rear -or back surface of the panel, has an enlarged portion 46 defining a locating shoulder 48 hearing against a fiat washer 50.

In accordance with the invention, I provide a permanent magnet 52, which constitutes an actuating element for the several reed switches 14 and which, as shown in FIG. 2, is disposed in position to traverse the several switches in closely spaced proximity thereto. The magnet 52, in the example of the invention shown in FIGS. 1-5, includes a recess, defining north and south poles 53, 55 respectively.

Manget 52 is mounted for rotatable adjustment upon the outer end of the arm 34. In the illustrated example, I show as one typical construction a fiat, circular support plate 56 to the underside of which the magnet 52 is welded or otherwise fixedly secured in position extendinng diametrically across the plate. The plate 56, on its top surface, is provided in the present instance with a series of radially disposed serrations. The serrations bear against the underside of the outer end portion of the arm 34, so as to permit the circular plate to be clampably engaged with the arm 34, whereby to hold the magnet in selected positions of rotary adjustment about the axis of a mounting stud 66 that is fixedly secured to the plate 56. The stud 60 extends through an opening provided in the arm 34, and passes through a clamping washer 62, against which bears a knurled clamp nut 64 threadedly engaged with the upstanding portion of the stud.

It will be readily perceived that the plate 56, with its fixedly attached magnet 52, can be adjusted about the axis of the stud, so as to locate the magnet in selected positions of angular adjustment about said axis, as for example in the full and dotted line positions shown in FIG. 3. In each position to which the magnet is so adjusted, the magnet can be fixedly secured against movement by turning the clamp nut 64 down against the washer 62. This draws plate 56 up against the arm 34, to retain the selected adjustment. 1

In use, and assuminga maximum duration of contact closure is desired for each of the several reed switches 14, one would adjust the magnet 52 to the position thereof shown in FIGS. 1 and 2, and in full lines in FIG. 3. In this position of the magnet, an imaginary line drawn between its poles will align longitudinally with each reed switch as it passes across the switch during rotation of the arm 34 about the stub shaft 38.

It has been found that in the above-described circumstances, the lines of magnetic force, extending longitudinally of the reed switch contacts, have their maximum effect in producing a switch closure of maximum duration. Conversely, perpendicularity of a line between the poles (see FIG. 4) will cause the closure of the reed switch to be of minimum duration.

Should the magnet be adjusted to any of various selected poistions midway between the FIG. 2 and FIG. 4 positions, the closure time for the reed switch will be correspondingly adjusted. Thus, the arrangement permits adjustments ranging from a maximum closure period caused by the magnet position of FIG. 2, to a minimum closure period caused by the magnet position of FIG. 4. Any of various positions occurring between these two extreme positions can be utilized advantageously.

It will be understood, in this regard, that the magnet could be so proportioned as to produce a simultaneous closure of more than one switch. Thus, it is possible to produce a make-before-break action, by so prop0rtioning the magnet in relation to the spacing between adjacent switches, as to cause one switch to close or make before the switch next preceding the same has opened.

In FIGURE 6, I provide a modified construction generally designated 10a, including a support panel 12a on which are mounted an annular outer bank of uniformly spaced reed switches 14a, annular inner bank of uniformly spaced switches 14]), and a single switch 140 disposed inwardly from the bank of switches 14:11.

In the illustrated example, there are 32 switches in the outer bank, four in the inner bank, and a single switch 14c. Switch 140 is in radial alignment with one of the switches 14b and one of the switches 140. This showing is purely exemplary, and I might use any relative proportions between the numbers of switches in the several banks. I may also use any number of banks. Thus, I might employ 100 switches in an outer bank, 50 in an intermediate bank, and ten in a third bank. Or, in three banks I might use 100* in an outer bank, ten in an inner bank, and one switch inwardly from the inner bank. As will.be recognized, the number of other possible arrangements is almost limitless.

Mounted on a center pin 38a to rotate on panel 12a about a center common to the banks of switches is a circular plate 34a which is in effect a commutator arm similar to arm 34. Aligned radially of the plate 34a are magnets 52a, 52b, and 520, spaced from the axis of rotation correspondingly to the switches 14a, 14b, and Me respectively. The magnets are similar to the magnet 52 of the first form of the invention. Further, they are mounted on the plate 34a similarly to the mounting of magnet 52 on arm 34, that is, the magnets are carried by studs similar to stud 60, and are capable of being individu-ally secured in selected positions of rotatable adjustment through the provision of clamp nuts 64a, 64b, and 640 respectively.

It will be understood that instead of a circular plate 34a, I may employ an arm like the arm 34, in the FIG- URE 6 device. Or, I may use a circular plate in the form of the invention shown in FIGURES l and 7. This might in fact be preferable in a device in which the magnet support means rotates at high speed, to provide a more elficient weight distribution and balance in the rotating mass, and also to reduce resistance to rotation that might otherwise be offered by air in the plane of rotation of the commutator arm.

In the FIGURE 6 arrangement, there will be eight closures of switches 14a for each closure of a switch 14b. There will be four closures of switches 14b and 32 closures of switches 14a for each closure of a switch 14c. The basic concept as described with reference to FIGURE 1 remains, of course, unchanged.

In FIGS. 7-9 there is illustrated a further modification. In this form of the invention, a special linkage has been devised for the purpose of producing a selected switch closure duration, that will progressively decrease through of the annular series of switches, and then increase through the next 90, decreasing once again through the third 90 or quadrant, and then increasing through the final quadrant in a single, complete 360 cycle of rotation of the commutator. In this form of the invention the commutator has been generally designated 32b and includes a wide, flat arm 34b the inner end of which is provided with a grommet or sleeve fixedly secured to the arm and having a set screw tightened against stub shaft 38. A support bridge 66 is affixed to the panel 12, in offset relation to the shaft 38.

A link 68, which may be formed from a length of stiff wire or rod material, has at one end an outwardly extending pintle 70 rotat-ably engaged in an opening formed in the bridge 66. At its other end, the link 68 has an inwardly turned end portion 72, which as shown in FIG. 9 is rotatably engaged in the outer end of a crank arm 74, the inner end of which is fixedly secured to a stud 76 through the provision of a set screw 78 carried by the crank arm. Stud 76 is rigid with a base plate 80, to which is welded or otherwise fixedly secured the magnet 52.

A grommet 82 is carried by the outer end of the arm 34a, and the stud 76 is rotatable in said grommet.

By reason of this arrangement, wherein the end or pintle 70 of the link 78 is offset from the axis of rotation of the arm 34b, it will be observed that as the arm 34b turns about its center, the crank arm 74 will be caused to rot-ate about the center defined by the stud 76. During each 360 cycle of rotation of the arm 34!), the crank 74 will likewise be caused to turn through 360 about the stud 76. The result will 'be that assuming that the arm when in full lines is in its starting position, a line between the poles of the magnet 52 will be parallel to the length of the reed switch immediately thereunder. This particular switch will thus have a maximum closure time.

As the arm begins its movement through 360, the magnet 52 will be caused to turn with the crank arm 74, so that the next reed switch will have a slightly shorter dwell time. The reed switch next following in the direction of rotation of the arm would have a still shorter closure time, and so on until the arm has passed through 90 to the dash-line position shown in FIG. 7. In this position, the line 'between the poles of magnet 52 will be disposed in perpendicular relation to the length of the reed switch 14 located thereunder, and the dwell time will be at its minimum.

From the dash-line position in FZIG. 7, continued clockwise rotation of the arm will now cause the magnet to produce a progressively increasing closure period for the reed switches during the next 90 of travel of the arm, that is, from the 12 oclock to 3 oclock position shown in FIG. 7. In the dash-dotted line position, for example, the magnet has just traversed a switch with the magnet positioned to produce closure of the contacts of the switch for a time period midway between the maximum and minimum.

It will be apparent that from the 3 oclock to the 6 oclock position, the switch closure time will be progressively decreased, and so on until the full 360 cycle is completed.

As previously noted, a circular plate like plate 34a could be used instead of arm 34b.

It will be apparent that there are many permanent magnet shapes that I might use. Those illustrated are purely exemplary of magnets that will act on the switches as desired, when disposed. parallel or at selected angles thereto.

It is believed apparent that the invention is not necessarily confined to the specific use or uses thereof described above, since it may be utilized for any purpose to which it may be suited. Nor is the invention to be necessarily limited to the specific construction illustrated and described, since such construction is only intended to be illustrative of the principles of operation and the means presently devised to carry out said principles, it being considered that the invention comprehends any changes in construction that may be permitted within the scope of the appended claims.

I claim:

1. A variable-dwell commutating magnetic switch construction comprising:

(a) a multiplicity of switches mounted to operate in following order along a predetermined path, each switch including a set of elongated reeds providing contacts extending over said path transversely thereof, said contacts being overlapped longitudinally in the area of crossing and being relatively flexed from normal positions thereof actuable in response to an external magnetic source to operate the switch; and

(b) a commutator for said switches including (1) permanent magnet support means mounted for movement adjacent said path, said means including a movable support arm, a support plate having a surface in confronting relation to a surface of the arm, a stud extending from the plate and axially shiftable in an opening of the arm, said plate being rotatable about the axis of the stud, and a clamping element movable axially of the stud against the opposite surface of the arm to shift the stud axially in a direction such that the confronting surfaces of the plate and arm are relatively moved into locking, face-to-face engagement in selected positions of rotary adjustment of the plate, and

(2) a permanent magnet carried by the support means for movement along said path in proximity to the switches for operating the same in said order, said magnet being mounted upon said plate for rotary adjustment therewith to at least first and second positions of angular adjustment of a straight line drawn between its poles in respect to said path, the lines of magnetic force of the magnet passing through the overlapped portions of the contacts longitudinally of said portions in said first position to maximize the duration of the flexure of the contacts from their normal positions, said lines of force in said second position extending transversely of the overlapped contact portions to minimize the duration of said flexure.

2. A variable-dwell commutating magnetic switch construction comprising:

(a) a multiplicity of switches mounted to operate in following order along a predetermined path, each switch including a set of elongated reeds providing contacts extending over said path transversely thereof, said contacts being overlapped longitudinally in the area of crossing and being relatively flexed from normal positions thereof actuable in response to an external magnetic source to operate the switch; and

(b) magnet support means comprising a commutator for said switches including (1) a movable support member, part at least of which travels along said path adjacent the several switches on movement of the member, a support plate having a surface in confronting relation to a surface of said support member, a stud extending from the plate and axially shiftable in an opening of said part of the support member, said plate being rotatable about the axis of the stud, and a clamping element movable axially of the stud against the opposite surface of the support member to shift the stud axially in a direction such that the confronting surfaces of the plate and support member are relatively moved into locking, face-to-face engagement in selected positions of rotary adjustment of the plate, and

(2) a permanent magnet carried. by said plate along said path in position to operate the several switches in said following order, said magnet and plate being mounted on the stud for rotatable adjustment through at least 90, the axis'of rotation of the magnet extending through a straight line drawn between the poles of the magnet, for angular adjustment of said line to at least first and second positions in respect to said path, the lines of magnetic force of the magnet passing through the overlapped portions of the contacts longitudinally of said. portions in said first position to maximize the duration of the flexure of the contacts from their normal positions, said lines of force in said second position extending transversely of the overlapped contact portions to minimize the duration of said flexure.

3. A variable-dwell commutating magnetic switch construction comprising:

(a) a multiplicity of reed switches angularly spaced about a common center, each of said switches being extended radially of said center, each switch including a set of elongated reeds providing contacts extending over said path transversely thereof, said contacts being overlapped longitudinally in the area of crossing and being relatively flexed from normal positions thereof actuable in response to an external magnetic source to operate the switch; and

(b) a commutator for said switches including (1) magnet support means comprising a support member movable about said center, said member extending adjacent the several switches in position to traverse the same when it is move-d about said center, a support plate having a roughened surface in confronting relation to a flat surface of said support member, a stud extending from the plate and axially shiftable in an opening of the member, said plate being rotatable about the axis of the stud, and a clamping element movable axially of the stud against the opposite surface of said member to shift the stud axially in a direction such that the confronting surfaces of the plate and support member are relatively moved into locking, faceto-face engagement in selected positions of rotary adjustment of the plate, and

(2) a permanent magnet carried by said plate in position to operate the switches in following order on said traverse of the switches, said mag net being mounted on said plate for rotatable adjustment therewith about a center passing through an imaginary straight line drawn medially between the poles of the magnet, said line being moved about the axis of magnet rotation, responsive to said adjustment of the magnet, between a first position in parallelism with switches traversed by said end of the arm, and a second position normal to the switches so traversed, the lines of magnetic force of the magnet passing through the overlapped portions of the contacts longitudinally of said portions in said first position to maximize the duration of the flexure of the contacts from their normal positions, said lines of force in said second position extending transversely of the overlapped contact portions to minimize the duration of said flexure.

4. A variable-dwell commutating magnetic switch construction comprising:

(a) a multiplicity of reed switches angularly spaced about a common center, each of said switches being extended radially from said center, said switches lying in a common plane, each switch including a set of elongated reeds providing contacts extending over said path transversely thereof, said contacts being overlapped longitudinally in the area of crossing and being relatively flexed from normal positions thereof 8 actuable in response to an external magnetic source to operate the switch; and

(b) a commutator for said switches including (1) magnet support means comprising a support member rotatable about said center on an axis normal to said plane, said member extending adjacent the several switches and traversing the same during rotatable movement of the member, a support plate having one face in confronting relation to one face of said member, a stud extending from the plate, the axis of the stud being parallel to said axis of rotation of the support member, the stud being axially shiftable in an opening of the support member and the plate being rotatable about said axis of the stud, and a clamping element movable along the stud axially thereof against the opposite face of the support member to shift the stud in an axial direction such that the confronting faces of the plate and arm are relatively moved into locking engagement with each other in selected positions to which the plate is rotatably adjusted, and

(2) a permanent magnet mounted on said plate in position to operate the switches in following order on traverse of the switches by the arm, said magnet having spaced poles lying in a plane parallel to the common plane of the switches whereby an imaginary straight line drawn between the poles will be in parallelism with said plane of the switches, the magnet being rotatable with the plate about said axis of the stud, said axis of the stud passing through said line medially between the poles of the magnet, said line being shift-able responsive to rotation of the magnet about the second axis, between a first position in parallelism with switches traversed by said member, and a second position normal to the switches so traversed, the lines of magnetic force of the magnet passing through the overlapped portions of the contacts longitudinally of said portions in said first position to maximize the duration of the flexure of the contacts from their normal positions, said lines of force in said second position extending transversely of the overlapped contact portions to minimize the duration of said flexure.

5. A variable-dwell commutating magnetic switch construction as in claim 4 wherein the angular distance between adjacent switches is selected to require, in all positions of adjustment of the magnet about the second axis, return of each switch to its normal condition subsequent to operation of the switch next following the same in the sense of the direction of rotation of said member.

6. A variable-dwell commutating magnetic switch construction as in claim 4 wherein said switches are arranged in a first annular bank, said construction further including at least one additional annular bank of switches concentric with the first bank, and a second magnet on said member arranged to operate the switches of the second bank, said second magnet being adjustable on the member similarly to but independently of the first named magnet.

7. A variable-dwell commutating magnetic switch construction comprising:

(a) a multiplicity of reed switches angularly spaced about a common center, each of said switches being extended radially from said center, said switches lying in a common plane, each switch including a set of contacts actuable in response to an external magnetic source to operate the switch; and

(b) a commutator for said switches including (1) a support member rotatable about said center on an axis normal to said plane, said member extending adjacent the several switches and traversing the same during rotatable movement of the member;

(2) a permanent magnet mounted on said member in position to operate the switches in following order on traverse of the switches by the arm, said magnet having spaced poles lying in a plane parallel to the common plane of the switches whereby an imaginary straight line drawn between the poles will be in parallelism with said plane of the switches, the magnet being rotatable on the arm about an axis parallel to the first axis and passing through said line medially between the poles of the magnet, said line being shiftable responsive to rotation of the magnet about the second axis, between a first position in parallelism with switches tra versed by said member, and a second position normal to the switches so traversed, and

(3) means to rotate the magnet continuously about the second axis responsive to rotation of said member about said first axis.

10 8. A variable-dwell commutating switch construction as in claim 7, wherein said magnet-rotating means includes a crank arm rotatable with the magnet and extending radially from the second axis, and a connecting 5 link pivotally attached to said crank arm and swinging about a center spaced from said first axis.

References Cited by the Examiner 10 UNITED STATES PATENTS 2,448,779 9/1948 Crise 20019 2,999,914 9/1961 Stanaway 200-19 3,087,030 4/1963 Shebanow 20019 3,133,173 5/1964 Vriens 200-37 15 3,158,710 11/1964 Paglee 20087 3,162,738 12/1964 Abramson et a1. 200-87 BERNARD A. GILHEANY, Primary Examiner.

20 B. DOBECK, Assistant Examiner. 

1. A VARIABLE-DWELL COMMUTATING MAGNETIC SWITCH CONSTRUCTION COMPRISING: (A) A MULTIPLICITY OF SWITCHES MOUNTED TO OPERATE IN FOLLOWING ORDER ALONG A PREDETERMINED PATH, EACH SWITCH INCLUDING A SET OF ELONGATED REEDS PROVIDING CONTACTS EXTENDING OVER SAID PATH TRANSVERSELY THEREOF, SAID CONTACTS BEING OVERLAPPED LONGITUDINALLY IN THE AREA OF CROSSING AND BEING RELATIVELY FLEXED FROM NORMAL POSITIONS THEREOF ACTUABLE IN RESPONSE TO AN EXTERNAL MAGNETIC SOURCE TO OPERATE THE SWITCH; AND (B) A COMMUTATOR FOR SAID SWITCHES INCLUDING (1) PERMANENT MAGNET SUPPORT MEANS MOUNTED FOR MOVEMENT ADJACENT SAID PATH, SAID MEANS INCLUDING A MOVABLE SUPPORT ARM, A SUPPORT PLATE HAVING A SURFACE IN CONFRONTING RELATION TO A SURFACE OF THE ARM, A STUD EXTENDING FROM THE PLATE AND AXIALLY SHIFTABLE IN AN OPENING OF THE ARM, SAID PLATE BEING ROTATABLE ABOUT THE AXIS OF THE STUD, AND A CLAMPING ELEMENT MOVABLE AXIALLY OF THE STUD AGAINST THE OPPOSITE SURFACE OF THE ARM TO SHIFT THE STUD AXIALLY IN A DIRECTION SUCH THAT THE CONFRONTING SURFACES OF THE PLATE AND ARM ARE RELATIVLEY MOVED INTO LOCKING, FACE-TO-FACE ENGAGEMENT IN SELECTED POSITIONS OF ROTARY ADJUSTMENT OF THE PLATE, AND (2) A PERMANENT MAGNET CARRIED BY THE SUPPORT MEANS FOR MOVEMENT ALONG SAID PATH IN PROXIMITY TO THE SWITCHES FOR OPERATING THE SAME IN SAID ORDER, SAID MAGNET BEING MOUNTED UPON SAID PLATE FOR ROTARY ADJUSTMENT THEREWITH TO AT LEAST FIRST AND SECOND POSITIONS OF ANGULAR ADJUSTMENT OF A STRAIGHT LINE DRAWN BETWEEN ITS POLES IN RESPECT TO SAID PATH, THE LINES OF MAGNETIC FORCE OF THE MAGNET PASSING THROUGH THE OVERLAPPED PORTIONS OF THE CONTACTS LONGITUDINALLY OF SAID PORTIONS IN SAID FIRST POSITION TO MAXIMIZE THE DURATION OF THE FLEXURE OF THE CONTACTS FROM THE NORMAL POSITIONS, SAID LINES OF FORCE IN SAID SECOND POSITION EXTENDING TRANSVERSELY OF THE OVERLAPPED CONTACT PORTIONS TO MINIMIZE THE DURATION OF SAID FLEXURE. 